Methods and uses of dissolved organic material fractions for binding metal ions

ABSTRACT

The present application discloses a method of binding a metal ion in water. The method comprises contacting the water with a fraction of dissolved organic material (DOM) to form a complex between the DOM fraction and the metal ion; and optionally separating the complex from the water. The present application also discloses a use of DOM for binding a metal ion in water.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority from U.S. provisional application nos. 62/377,323 filed on Aug. 19, 2016 and 62/513,018 filed on May 31, 2017, the contents of each of which are incorporated herein by reference in their entirety.

FIELD

The present application relates to methods of binding metal ions. For example, the present application relates to methods and uses of dissolved organic material for binding a metal ion in water such as wastewater.

BACKGROUND

Mercury (Hg) is a toxic metal that can disrupt natural enzymatic processes and cause cellular stress^(1a). In addition to being toxic as inorganic Hg^(II), humans and wildlife are also exposed to the potent neurotoxin monomethylmercury (MMHg). Upon deposition from the atmosphere, Hg^(II) first interacts with inorganic and organic ligands under oxic conditions. Furthermore, whereas microbial Hg^(II) methylation to toxic MMHg occurs under anoxic conditions, recent reports suggest that methylation may not solely be limited to anoxic microbial habitats^(1b). Therefore, a comprehensive approach to studying Hg^(II) pathways from the atmosphere to methylation sites requires that Hg^(II) speciation and bioavailability to microbial cells be studied over a wide range of environments, including oxic freshwaters²¹³. Such studies, characterizing dissolved organic matter (DOM) on a molecular level and how it interacts with Hg^(II) are not known to have previously been disclosed. DOM is a complex mixture of heterogeneous material deriving from a variety of autochthonous and allochthonous sources that can, for example, act as a microbial nutrient source, affect light penetration in solution and chelate metals³⁻⁷.

DOM has a very diverse and dynamic composition that, while not wishing to be limited by theory, may interact with Hg^(II) in several ways. First, the binding of Hg^(II) to DOM can decrease its mobility and bioavailability via the formation of metastable structures with large hydrophobic DOM molecules⁵⁻⁷. Alternatively, the binding of Hg to small molecules such as amino acids or peptides (e.g., cysteine or glutathione (GSH)) has been shown to increase Hg bioavailability⁸. DOM hydrogenation and oxygenation has been previously correlated to microbial uptake of DOM nutrient sources⁹. For example, DOM high in hydrogenated (larger H/C, lower O/C) nitrogen containing compounds correspond to more bioavailable amino acid rich material whereas highly oxygenated (larger O/C, lower H/C) carbon sources are less favorable microbial nutrient sources⁹⁻¹⁹. Sulfides (free or associated with DOM) are predicted to be an important ligand for Hg^(II) under anoxic conditions that also favor MMHg formation, but strong interactions between Hg^(II) and DOM in oxic waters can affect subsequent binding to sulfides⁷. This is important in stratified aquatic ecosystems where an oxic water column overlies an anoxic zone¹¹⁻¹⁴. The binding of Hg to DOM is controlled by a group of homologous structures within DOM containing reduced sulfur species (R-SH), but understanding how composition and size of organic ligands influence Hg bioavailability has also been lacking¹⁵⁻¹⁹.

SUMMARY

Accordingly, the present application includes a method of binding a metal ion in water, the method comprising:

-   -   contacting the water with a fraction of dissolved organic         material (DOM) to form a complex between the DOM fraction and         the metal ion; and     -   optionally separating the complex from the water.

The present application also includes a use of a fraction of dissolved organic material (DOM) for binding a metal ion in water.

Other features and advantages of the present application will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the application, are given by way of illustration only and the scope of the claims should not be limited by these embodiments, but should be given the broadest interpretation consistent with the description as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

The present application will now be described in greater detail with reference to the drawings, in which:

FIG. 1 is a plot showing bioassay response in bioluminescence (cps) for various embodiments of an example of the present application based on glass (dark grey) and Teflon (light grey) scintillation vials.

FIG. 2 is a plot showing normalized bioluminescence response from 1-20 ppm dissolved organic carbon (DOC) for Suwannee River (SRFA) samples. The first through third bars from the left indicate 250 pM, 100 pM and 0 pM, respectively of HgNO₃ added in the absence of ligands.

FIG. 3 is a plot showing normalized bioluminescence response from 1-20 ppm DOC for Pony Lake (PLFA) samples. The first through third bars from the left indicate 250 pM, 100 pM and 0 pM, respectively of HgNO₃ added in the absence of ligands.

FIG. 4 shows an asymmetrical flow field-flow fractionation (AF4) fractogram at 254 nm of SRFA (light grey) and PLFA (darker grey) with vertical bars indicating the boundaries between low molecular weight (LMW; 300-900 Da); medium molecular weight (MMW; 900-1800 Da) and high molecular weight (HMW; 1800-3500 Da) fractions.

FIG. 5 is a plot showing the response of the fractions in FIG. 4 to 250 pM of HgNO₃ (fifth to seventh bars from the left; SRFA and ninth to eleventh bars from the left; PLFA) in comparison to the bioassay response to 1 ppm unfractionated SRFA and PLFA (fourth and eighth bars from the left, respectively). The first through third bars from the left indicate 250 pM, 100 pM and 0 pM, respectively of HgNO₃ added in the absence of ligands.

FIG. 6 shows Fourier-transform ion cyclotron resonance mass spectrometry (FT ICR-MS) weighted elemental contribution within bulk (dotted) and AF4 size fractions of SRFA (left four bars) and PLFA (right four bars) for carbon. Asterisk represents a significant difference (p<0.05) in composition between LMW and HMW fractions for both SRFA and PLFA.

FIG. 7 shows FT ICR-MS weighted elemental contribution within bulk (dotted) and AF4 size fractions of SRFA (left four bars) and PLFA (right four bars) for hydrogen. Asterisk represents a significant difference (p<0.05) in composition between LMW and HMW fractions for both SRFA and PLFA.

FIG. 8 shows FT ICR-MS weighted elemental contribution within bulk (dotted) and AF4 size fractions of SRFA (left four bars) and PLFA (right four bars) for oxygen. Asterisk represents a significant difference (p<0.05) in composition between LMW and HMW fractions for both SRFA and PLFA.

FIG. 9 shows FT ICR-MS weighted elemental contribution within bulk (dotted) and AF4 size fractions of SRFA (left four bars) and PLFA (right four bars) for nitrogen.

FIG. 10 shows FT ICR-MS weighted elemental contribution within bulk (dotted) and AF4 size fractions of SRFA (left four bars) and PLFA (right four bars) for sulfur.

FIG. 11 is a plot showing the inverse relationships between normalized bioassays and corresponding aromaticity index (AI) of each size fraction and unfractionated sample in FIGS. 6-10.

FIG. 12 shows FT ICR-MS spectra of SRFA (top) and PLFA (bottom) based on an average of 200 scans and corresponding 3D van Krevelen diagrams (insert graphs). In colored figures, the van Krevelen diagram shade is based on the absolute intensity of the corresponding peak (light to dark increasing in intensity).

FIG. 13 shows principal component analysis (PCA) of atomic ratios and size fractions by SRFA (triangles) and PLFA (circles).

FIG. 14 shows principal component 1 (PC1) eigenvalues vs. normalized bioluminescence response for SRFA (top) and PLFA (bottom).

FIG. 15 shows the relative abundance of various ions for Hg(Cys)₂ complexes detected (top) in comparison to the theoretical isotopic distribution (bottom) according to an example of the present application.

FIG. 16 shows mass spectra and van Krevelen plots (insets) for phytoplankton derived DOM from Chlorella (left), Chlamydomonas (middle) and Euglena (right) according to examples of the present application.

FIG. 17 shows a comparison between the observed (top) and predicted (bottom) isotopic distributions for the ²⁰²Hg peak found in phytoplankton-derived DOM Hg complexes from Chlorella (left), Chlamydomonas (middle) and Euglena (right) according to an example of the present application.

FIG. 18 shows mass spectra for phytoplankton-derived DOM Hg complexes from Chlorella (left), Chlamydomonas (middle) and Euglena (right) according to an example of the present application. Boxes indicate the location along the m/z axis left to right, the formulae: C₃₇H₆₆OHg, C₈H₁₅N₂Hg and C₁₀H₁₁O₂HgS.

FIG. 19 is a plot of AF4 used to separate DOM from SRFA, Chlorella vulgaris, Chlamydomonas reinhardtii, and Euglena gracilis according to examples of the present application with vertical bars indicating the boundaries between low molecular weight (LMW; 300-900 Da); medium molecular weight (MMW; 900-1800 Da) and high molecular weight (HMW; 1800-3500 Da) fractions.

FIG. 20 is a plot of bioluminescence response as a function of the fractions in FIG. 19 exposed to 250 pM of Hg(NO₃)₂ according to examples of the present application (4-6 bars from left: SRFA; 7-9 bars from left: Chlorella; 10-12 bars from left: Chlamydomonas; 13-15 bars from left: Euglena). The first through third bars from the left indicate 250 pM, 100 pM and 0 pM, respectively of HgNO₃ added in the absence of ligands.

FIG. 21 shows a comparison between observed (top) vs theoretical (bottom) isotopic distribution confirming ¹³C isotope of the molecule C₃₈H₇₆ON to reinforce accurate formula assignment.

FIG. 22 shows a comparison between observed (top) vs theoretical (bottom) isotopic distribution confirming ³⁴S isotope of the molecule C₂₂H₄₇O₈NS to reinforce accurate formula assignment.

FIG. 23 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Chlorella exposed to a standard (16:8 h) light regime in the absence of Hg according to an example of the present application.

FIG. 24 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Chlorella exposed to a standard (16:8 h) light regime in the presence of Hg according to an example of the present application.

FIG. 25 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Chlorella exposed to a high (20:4 h) light regime in the absence of Hg according to an example of the present application.

FIG. 26 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Chlorella exposed to a high (20:4 h) light regime in the presence of Hg according to an example of the present application.

FIG. 27 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Chlamydomonas exposed to a standard (16:8 h) light regime in the absence of Hg according to an example of the present application.

FIG. 28 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Chlamydomonas exposed to a standard (16:8 h) light regime in the presence of Hg according to an example of the present application.

FIG. 29 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Chlamydomonas exposed to a high (20:4 h) light regime in the absence of Hg according to an example of the present application.

FIG. 30 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Chlamydomonas exposed to a high (20:4 h) light regime in the presence of Hg according to an example of the present application.

FIG. 31 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Scenedesmus exposed to a standard (16:8 h) light regime in the absence of Hg according to an example of the present application.

FIG. 32 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Scenedesmus exposed to a standard (16:8 h) light regime in the presence of Hg according to an example of the present application.

FIG. 33 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Scenedesmus exposed to a high (20:4 h) light regime in the absence of Hg according to an example of the present application.

FIG. 34 shows a mass spectrum of the DOM composition and a Kendrick mass defect plot to display homologous CH₂ shifts indicative of DOM (inset) for Scenedesmus exposed to a high (20:4 h) light regime in the presence of Hg according to an example of the present application.

FIG. 35 shows plots of weighted average molecular characteristics (clockwise from top left: O/C, H/C, N/C, S/C, m/z, AI mod, NOSC, % S, % O, % N, % H and % C) of DOM produced from Chlorella (black bars), Chlamydomonas (light grey bars), and Scenedesmus (white bars) exposed to a standard (16:8 h) light regime (left three bars of each plot) or high (20:4 h) light regime (right three bars of each plot according to examples of the present application.

FIG. 36 shows van Krevelen diagrams of phytoplankton-derived DOM from Chlorella grown at 16:8 h (top) in comparison to 20:4 h (bottom) light:dark cycles according to examples of the present application. Darker shades correspond to molecules with greater m/z and larger point sizes correspond to greater peak intensity.

FIG. 37 shows van Krevelen diagrams of phytoplankton-derived DOM from Chlamydomonas grown at 16:8 h (top) in comparison to 20:4 h (bottom) light:dark cycles according to examples of the present application. Darker shades correspond to molecules with greater m/z and larger point sizes correspond to greater peak intensity.

FIG. 38 shows van Krevelen diagrams of phytoplankton-derived DOM from Scenedesmus grown at 16:8 h (top) in comparison to 20:4 h (bottom) light:dark cycles according to examples of the present application. Darker shades correspond to molecules with greater m/z and larger point sizes correspond to greater peak intensity.

FIG. 39 shows compound classes based on van Krevelen diagrams portraying the relative abundance (%) of from left to right: lignin, protein, unsaturated hydrocarbons, lipids, carbohydrates, tannins and aromatic structures released by Chlorella (left), Chlamydomonas (middle) and Scenedesmus (right) grown at 16:8 h (top) in comparison to 20:4 h (bottom) light:dark cycles according to examples of the present application. Error bars for both 16:8 h and 20:4 h light:dark cycles are based on biological duplicates (n=2).

FIG. 40 shows detection of a Hg:Cysteine [HgC₆H₁₃N₂O₄S₂] complex at a 1:2 molar ratio and six detected Hg isotopologues (²⁰⁴Hg, ²⁰²Hg, ²⁰¹Hg, ²⁰⁰Hg, ¹⁹⁸Hg, and ¹⁹⁶Hg) (top) according to examples of the present application in comparison to the theoretical isotopic distribution (bottom); relative abundances of each isotope agree. Exact mass comparison also revealed mass accuracy of ±5 ppm for Hg isotopes.

FIG. 41 shows mass spectra of DOM from Chlamydomonas in the absence (top) and presence (bottom) of Hg indicating the presence of Hg isotopologues after the Hg addition.

FIG. 42 shows identified Hg containing DOM for Chlorella, (top) Chlamydomonas (third from top) and Scenedesmus (second from bottom) according to examples of the present application, in comparison to corresponding spectra of the theoretical isotopic distribution (second from top, third from bottom and bottom, respectively).

FIG. 43 shows plots wherein based on exact mass and isotopic conformation, the abundance of Hg binding DOM at 16:8 h (top) and 20:4 h (bottom) according to examples of the present application were grouped based on generic molecular formula. White bars: Chlorella, grey bars: Chlamydomonas, and black bars: Scenedesmus.

FIG. 44 shows two-way hierarchical cluster analysis based on structural properties of Hg binding DOM at a 16:8 h light cycle according to an example of the present application. A Spearman's correlation matrix also portrays the overall weight of each molecular group to a structural property where darker colorations indicate a stronger correlation.

FIG. 45 shows two-way hierarchical cluster analysis based on structural properties of Hg binding DOM at a 20:4 h light cycle according to examples of the present application. A Spearman's correlation matrix also portrays the overall weight of each molecular group to a structural property where darker colorations indicate a stronger correlation.

FIG. 46 shows an experimental mass spectrum (top) compared to the corresponding theoretical mass spectrum (bottom) for the identification of a putative isomer of the bacterial siderophore carboxymycobactins with an empirical formula of HgC₃₇H₅₄N₅O₁₃ found in Chlorella 20:4 h cultures according to an example of the present application.

FIG. 47 shows an observed mass spectrum (top) compared to the corresponding theoretical mass spectrum (bottom) for possible isomers of Hg binding ligands based on exact mass and Hg isotopic distributions of acinetoferrin with an empirical formula of C₃₂H₅₄N₅O₁₀Hg according to an example of the present application.

FIG. 48 shows an observed mass spectrum (top) compared to the corresponding theoretical mass spectrum (bottom) for possible isomers of Hg binding ligands based on exact mass and Hg isotopic distributions of desferrioxamine G1 with an empirical formula of C₂₇H₄₉N₆O₁₀Hg+C₄H₇NO+H₂O+Hg according to an example of the present application.

FIG. 49 shows an observed mass spectrum (top) compared to the corresponding theoretical mass spectrum (bottom) for possible isomers of Hg binding ligands based on exact mass and Hg isotopic distributions of cyclic trichirsobactin with an empirical formula of C₄₁H₅₇N₉O₁₂+Hg according to an example of the present application.

FIG. 50 shows an observed mass spectrum (top) compared to the corresponding theoretical mass spectrum (bottom) for possible isomers of Hg binding ligands based on exact mass and Hg isotopic distributions of carboxymycobactin with an empirical formula of C₂₉H₃₂N₅O₁₃+Hg according to an example of the present application.

FIG. 51 shows an observed mass spectrum (top) compared to the corresponding theoretical mass spectrum (bottom) for possible isomers of Hg binding ligands based on exact mass and Hg isotopic distributions of exochelin with an empirical formula of C₂₇H₅₃N₁₀O₁₂+Hg according to an example of the present application.

FIG. 52 shows the effect of DOM concentration on Hg mobility for from left to right: Chlamydomonas reinhardttii, Scenedesmus obliguus, Chlorella vulgaris and Euglena gracilis according to examples of the present application under aerobic (top) and anaerobic (bottom) conditions.

FIG. 53 shows the effect of a DOM concentration of 1 ppm (left) compared to a DOM concentration of 30 ppm (right) according to examples of the present application on the production and release of DOM molecules of various molecular weights by Euglena gracilis.

FIG. 54 shows an observed mass spectrum (top) compared to the corresponding predicted mass spectrum (bottom) for oligopeptides—Cd complex according to an example of the present application.

FIG. 55 shows an observed mass spectrum (top) compared to the corresponding predicted mass spectrum (bottom) for bacteriohopanetetrol cyclitol ether—Cd complex according to an example of the present application.

FIG. 56 shows an observed mass spectrum (top) compared to the corresponding predicted mass spectrum (bottom) for Azaspiracid-3-Cd complex according to an example of the present application.

FIG. 57 shows an observed mass spectrum (top) compared to the corresponding predicted mass spectrum (bottom) for Brunsvicamide A—Cd complex according to an example of the present application.

DETAILED DESCRIPTION I. Definitions

Unless otherwise indicated, the definitions and embodiments described in this and other sections are intended to be applicable to all embodiments and aspects of the present application herein described for which they are suitable as would be understood by a person skilled in the art.

In understanding the scope of the present application, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. The term “consisting” and its derivatives, as used herein, are intended to be closed terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The term “consisting essentially of”, as used herein, is intended to specify the presence of the stated features, elements, components, groups, integers, and/or steps as well as those that do not materially affect the basic and novel characteristic(s) of features, elements, components, groups, integers, and/or steps.

As used in this application, the singular forms “a”, “an” and “the” include plural references unless the content clearly dictates otherwise.

In embodiments comprising an “additional” or “second” component, the second component as used herein is different from the other components or first component. A “third” component is different from the other, first, and second components, and further enumerated or “additional” components are similarly different.

II. Methods and Uses

Dissolved organic matter (DOM) is a dynamic ligand with properties that can govern the fate of mercury in natural systems. Whereas the production of monomethylmercury occurs under anoxic conditions, Hg^(II) first interacts with DOM under oxic conditions upon deposition from the atmosphere but studies investigating such interactions have been scarce. The present examples investigated the role of DOM (Suwannee River (SRFA) and Pony Lake (PLFA) fulvic acids), on Hg bioavailability using a multi-pronged approach relying on asymmetrical flow field-flow fractionation for DOM molecular weight separation, high resolution mass spectrometry for resolved compositional assessment, coupled to a whole-cell biosensor designed to quantify Hg^(II) uptake. It was shown that size fraction affects Hg^(II) bioavailability wherein lower molecular weight (MW) size fractions of SRFA abundant in small aliphatic material favors Hg^(II) uptake, while not wishing to be limited by theory, supporting the role for low molecular weight (LMW) compounds of DOM acting as an shuttle to microorganisms. High molecular weight (HMW: 1800-3500 Da) fractions made up of larger aromatic material significantly reduced Hg bioavailability for both SRFA and PLFA (p<0.05). The present examples demonstrated the usefulness of LMW aliphatic DOM enhancing Hg^(II) bioavailability in oxic environments suggesting, while not limited by theory, that differences in Hg^(II) bioavailability are not solely driven by nitrogen and sulfur content, but also by MW and aromaticity characteristics.

Accordingly, the present application includes a method of binding a metal ion (or species) in water, the method comprising:

-   -   contacting the water with a fraction of dissolved organic         material (DOM) to form a complex between the DOM fraction and         the metal ion; and     -   optionally separating the complex from the water.

The term “water” as used herein includes water in the form of a solution, suspension or slurry.

The term “hydrate form” as used herein refers to a substance that contains water in its solid form optionally its crystalline form.

The fraction of DOM can be any suitable fraction of DOM. For example, in the studies of the present disclosure, a significant increase in cellular mercury mobilization was observed when microorganisms were exposed to a low molecular weight organic compound fraction of the DOM. Accordingly, in an embodiment, the fraction of DOM is a low molecular weight organic compound fraction of the DOM (LMW-DOM). In another embodiment, the LMW-DOM contains molecular weights ranging from 150-900 or 300-900 Da. In another embodiment, the LMW-DOM contains molecular weights from at least 100, 150, 200, 250, 300, 350 or 400 Da. In another embodiment, the LMW-DOM contains molecular weights to at most 700, 750, 800, 850 or 900 Da. In an embodiment, the LMW-DOM contains a compound that is 3-methyldioxyindole, bellendine, linoleoyl, gluconapin, N-acetylleucyl-leucyl-methionianal, am inopentol, momordicilin, sulfanilamide, dihydroxypentatriaconta-2,4-dienoic acid, an oligo peptide (e.g. Ala-Thr-Leu-His; L-leucyl-L-asparaginylglycyl-L-lysyl-L-alanyl-L-leucyl-L-valyl-L-glutamic acid; L-leucyl-L-asparaginylglycyl-L-lysyl-L-alanyl-L-leucyl-L-valyl-L-glutamic acid; and/or L-valyl-L-asparaginyl-L-isoleucyl-L-glutam inyl-L-lysyl-L-α-glutam yl-L-isoleucine), 2-hydroxyheptanoic acid, (E)-penta-1,3-dien-2-ol, a diglyceride, glycerol triaprylate, 5,7,3′,4′-tetrahydroxy-3,6,5′-trimethoxyflavone, 9-octadecenoic acid, 1,2,3,4-tetrakis-o-(4-nitrobenzoyl)pentopyranose, ceramide, cefsulodin monobactam, 2,7,9-tricarboxypyrrolo(2,3-f)quinoline-4-ol-5-one, tetradecane-1,1-(O-alpha-D-glucopyranosyl)-3-keto-(1,25R,27R)-octacosanetriol, 2,4-bis[4,5-bis(pentylam ino)isoquinolin-1-yl]cyclobutane-1,3-dione, bacteriohopanetetrol cyclitol ether, azaspiracid-3, brunsvicamide A, siderochelin A, benarthin, chrysobactin, dihydroxybenzoic acid, rhizobactin, schizokinen, desferrioxamine, cyclic trichrisobactin, carboxymycobactin, exochelin, vibrioferrin, acinetoferrin, ferrioxamine or mixtures thereof. In an embodiment, the LMW-DOM contains a compound that is siderochelin A, benarthin, chrysobactin, dihydroxybenzoic acid, rhizobactin, schizokinen, desferrioxamine, cyclic trichrisobactin, carboxymycobactin, exochelin, vibrioferrin, acinetoferrin, ferrioxamine or mixtures thereof. In some embodiments, the solid form of the compound is a hydrate form thereof. It will be appreciated by a person skilled in the art that the identity of the compounds in the DOM may depend, for example, on the source of (e.g. the species of a microorganism producing) the DOM and therefore the embodiments of the present application may be varied accordingly.

Alternatively, by using a high molecular weight organic compound fraction of the DOM (HMW-DOM), the resulting non-labile complexes of the metal and the HMW-DOM are less bioavailable and can be separated through methods which make use of this property. A person skilled in the art could readily select such a method with reference to the present application and in light of common general knowledge such as known methods. Accordingly, in another embodiment of the present application, the fraction of DOM is a high molecular weight organic compound fraction of the DOM (HMW-DOM). In a further embodiment, the HMW-DOM contains molecular weights ranging from 1800-3500 Da or up to 1 μm.

In another embodiment of the present application, the fraction of DOM is a medium molecular weight organic compound fraction of the DOM (MMW-DOM). In a further embodiment, the MMW-DOM contains molecular weights ranging from 900-1800 Da.

Using a technique such as the high resolution mass spectrometry (HRMS) used in the examples of the present application can provide structural information such as mass to charge ratio about DOM compounds that readily bind metal ions such as Hg²⁺. Fractionation can optionally subsequently be applied, for example, to separate homologous groups of metal-ion complexing DOM fractions.

The methods of binding metal ions in water can be used for any suitable use wherein it is desired to bind a metal ion in water. For example, the methods may be used for the remediation of wastewater as well as for other water treatment and water purification applications. In an embodiment, the method is for remediation of wastewater having a metal ion to be removed and the water is wastewater. The wastewater can be any suitable wastewater. For example, the wastewater can be domestic wastewater, urban wastewater, industrial wastewater or combinations thereof. The term “industrial wastewater” includes any suitable water that contains metal ions and is waste from industry. For example, the industrial wastewater can comprise metal processing effluent or wastewater from electroplating processes. For example, wastewater stemming from the grinding of mineral and sediment can include dissolved metals such as divalent metals, for example, mercury which can be bound in the methods of the present application. Accordingly, in an embodiment, the industrial wastewater comprises effluent from a mining operation. The methods of the present application can also be used to capture a metal ion of interest from the water. For example, so that the metal ion can be converted into the metal.

In an embodiment, the complex is separated from the water. The method of separation can involve any suitable means of separation and will depend, for example, on the method by which the water is contacted with the DOM fraction. In an embodiment, the separation comprises contacting the complex with a microorganism to sequester the complex. The microorganism can be any suitable microorganism that can uptake (sequester) the complex. For example, the studies of the present application have tested the gram-negative bacteria E. coli but any other suitable microorganism can be used.

A person skilled in the art can select a suitable means for contacting the water with the DOM fraction in the methods of the present application.

The terms “dissolved organic matter” or DOM as used herein refer to a ubiquitous mixture of complex organic molecules that can be operationally defined as material that passes filter pores (e.g. of 1.0, 0.7, 0.45 or 0.2 μm pore sizes). DOM can include biomolecules such as lipids, peptides, proteins, amino acids, amino sugars, carbohydrates, lignin, tannins, condensed aromatics and saturated or unsaturated hydrocarbons. The composition of a particular DOM will depend, for example, on the source of the DOM. For example, any living or dead organism found in water or on land produces DOM. Such organisms include all phytoplankton, microbes and fungi. Living organisms can, for example, produce DOM as a result of metabolic waste. The decomposition of dead materials such as plants and trees (or parts thereof such as leaves) and terrestrial and aquatic organisms also produces DOM. The terms “dissolved organic matter” or “DOM” as used herein include DOM produced by all such natural sources as well as DOM or components thereof (i.e. one or more compounds found in DOM) that has been chemically synthesized. DOM from natural sources includes DOM collected from the environment as well as DOM which has been obtained from cultured organisms or parts thereof.

Accordingly, in an embodiment, the DOM is from phytoplankton. In another embodiment, the phytoplankton is a Chlorella sp., a Chlamydomonas sp., a Euglena sp., a diatom, a cyanobacteria, a protist or mixtures thereof. In a further embodiment, the phytoplankton is a Euglena sp. It is an embodiment that the phytoplankton is Chlorella vulgaris, Chlamydomonas reinhardtii, Euglena gracilis, Euglena mutabilis, Scenedesmus obliquus, Thalassiosira weissflogii or combinations thereof. In an embodiment, the phytoplankton is Chlorella (e.g. Chlorella vulgaris). In another embodiment, the phytoplankton is Chlamydomonas (e.g. Chlamydomonas reinhardtii). In a further embodiment, the phytoplankton is Euglena (e.g. Euglena gracilis or Euglena mutabilis). In another embodiment, the phytoplankton is Scenedesmus (e.g. Scenedesmus obliquus). In a further embodiment, the phytoplankton is Thalassiosira (e.g. Thalassiosira weissflogii). In another embodiment, the phytoplankton is Euglena gracilis, Euglena mutabilis or combinations thereof. In a further embodiment, the phytoplankton comprises, consists essentially of or consists of Euglena gracilis.

In another embodiment of the present application, the DOM (or the fraction thereof) is chemically synthesized. The chemically synthesized DOM can be synthesized by known methods or obtained from a commercial source.

In a further embodiment, the DOM fraction comprises, consists essentially of or consists of hydrogenated nitrogen containing compounds, wherein the hydrogen to carbon elemental ratio (H/C) of the compounds is greater than 1.65 (i.e. the cut-off for lipid and protein material). In the studies of the present disclosure, it was observed that hydrogenated DOM preferentially facilitates uptake as opposed to highly oxygenated DOM components. Accordingly, use of a DOM fraction that comprises, consists essentially of or consists of (e.g. that is enriched in) such compounds may facilitate uptake by microorganisms in embodiments wherein the separation is carried out by such a means.

In some embodiments, the DOM fraction is isolated from DOM. The DOM fraction can be isolated from DOM by any suitable means. In an embodiment, the DOM fraction is isolated from DOM by field-flow filtration, ultrafiltration or ultracentrifugation. In another embodiment, the DOM fraction is isolated from DOM by a method comprising field-flow filtration.

The DOM can optionally be produced under conditions suitable to obtain an increased percentage of one or more desired metal ion-binding compounds in the DOM fraction. For example, the conditions can comprise growing a culture of phytoplankton under conditions suitable to obtain the increased percentage of one or more desired metal ion-binding compounds in the DOM fraction. Such enhanced production can be influenced by culture conditions such as but not limited to medium, temperature, light, pH, ionic strength and metal concentrations. Accordingly, in an embodiment, the conditions comprise one or more of a desired medium, temperature, light, pH, ionic strength and metal concentration. For example, the generation of reactive oxygen species (ROS) and metabolic stress can induce an increase of antioxidants such as cysteine (Cys) and glutathione (GSH). Therefore, an increase in culturing metals, temperatures and/or light intensity or duration (within ranges tolerable to the phytoplankton) induces LMW compounds. The increase in light could also cause photodegradation of larger molecular weight compounds into smaller molecular weight compounds. Similarly, a decrease in culture pH could also cause degradation of larger molecular weight DOM compounds into smaller subunits. The exposure of phytoplankton cultures to non-lethal metal concentrations can act as a selective pressure wherein tolerant cells exhibit changes in peptide and amino acid composition and concentration. In another embodiment of the present application, the conditions comprise varying the light regime. In a further embodiment, the light regime is 16:8 h light:dark. In another embodiment of the present application, the light regime is 20:4 h light:dark.

The metal ion can be any suitable metal ion which forms a complex with the DOM fraction. The expressions “form a complex between the DOM fraction and the metal ion” and “metal ion which forms a complex with the DOM fraction” as used herein refers to forming a complex between the metal ion and at least one compound that is a component of the DOM fraction. The metal ion can be an anionic or cationic metal such as arsenic, rare earth elements, uranium and radionuclides. It will be appreciated by a person skilled in the art that the DOM fraction can include compounds with heteroatoms such as nitrogen (N), oxygen (O) and sulfur (S) that are capable of binding suitable metal ions. A DOM fraction can be selected for binding a particular metal or class thereof. For example, type A metals typically form more stable complexes with O- and N-containing ligands whereas Type-B metals typically form more stable complexes with S-containing ligands and metals are known to exhibit behaviour intermediate between Type A and Type B metals. In some embodiments, the metal is a transition metal. In some embodiments, the metal is a metal ion (i.e. M²⁺) and optionally Hg²⁺ or another metal that shows similar binding to heteroatoms (e.g. N, O and S) such as Cd²⁺, Zn²⁺, Co²⁺, Ni²⁺ or Pb²⁺. In another embodiment, the metal ion is a rare earth element, a divalent metal, a transition metal, or a divalent transition metal. In another embodiment, the metal ion is Hg²⁺. In another embodiment, of the present application, the metal ion is Cd²⁺.

The present application also includes a use of a fraction of dissolved organic material for binding a metal ion in water.

It will be appreciated by a person skilled in the art that embodiments of the uses of the present disclosure can be varied as described herein for the methods of the present disclosure.

The following non-limiting examples are illustrative of the present application:

EXAMPLES Example 1: The Role of Dissolved Organic Matter Size Fractions and Composition on Aerobic Mercury Uptake

To evaluate the role that DOM molecular weight (MW) and composition have on Hg bioavailability, a multi-pronged approach was developed, which relied on the use of asymmetrical flow field-flow fractionation (AF4) to separate DOM based on molecular weight, Fourier transform ion cyclotron mass spectrometry (FT ICR-MS) for resolved compositional assessment of MW fractions, and a whole-cell biosensor to investigate how size and composition of organic ligands influence Hg^(II) bioavailability under oxic conditions. Using these techniques in a multi-pronged approach, two fulvic acid reference standards from the Suwannee River (dominated by allochthonous inputs) and from Pony Lake (microbially based Antarctic aquatic ecosystem) were compared to study how DOM size fractions and composition influence Hg^(II) bioavailability.

I. Materials and Methods

(a) Standards and Asymmetrical Flow Field-Flow Fractionation

SRFA and PLFA were obtained from International Humic Substances Society, dissolved in ultrapure water (MQW; 18 mΩ), and filtered through a 0.7 μm glass fiber filter. Whereas SRFA and PLFA were subject to a variety of purification treatments, these standards served as a suitable DOM source for initial investigations into the role of DOM MW and structure influencing Hg bioavailability and used widely as reference materials to study metal bioavailability²⁰. The AF2000 Focus fractionation system (Postnova Analytics) with an on-line UV-visible spectrophotometer (Shimadzu SPD-M20A) and fraction collector (Varian ProStar 701) were used to isolate DOM size fractions. A 300 Da polyethersulfonate (PES, Postnova Analytics) with flow setting of 0.25, 2.2 and 2.45 mL min⁻¹ for axial, focus and cross flows, respectively. A calibration solution of macromolecular proteins was utilized to calibrate molecular weight of SRFA and PLFA²¹⁻²³. Approximately 2 mL of 200 ppm-C SRFA and PLFA were injected into the 300 μL sample loop and fractions were collected during the elution stage at 1 min intervals. Dissolved organic carbon (DOC) concentrations of each size fraction were determined using a UV-Visible absorbance at 254 nm where a calibration curve of known SRFA and PLFA concentrations and corresponding UV-Visible absorbance values were determined. Low (LMW 300-900 Da), medium (MMW 900-1800 Da) and high MW (HMW 1800-3500 Da) molecular weight fractions were collected for further analyses. LMW and MMW fractions coincided with the peak maxima in the AF4 fractogram for both SRFA and PLFA, respectively.

(b) Bioreporter Assay

An E. coli whole-cell biosensor was used to evaluate Hg^(II) bioavailability²⁴ where assay conditions were described in Chiasson-Gould et al. (2014)²⁵. Cultures were obtained from a single plate colony and inoculated in 5 mL of lysogeny broth (LB) in the presence of kanamycin at 37° C. for 6-7 h until log phase. Fifty microliters of the culture were transferred to a 25 mL serum bottle containing 5 mL of glucose minimal media (GMM) and incubated overnight. In the morning, 20 mL of fresh GMM was added and the cells were incubated for 2 h with shaking. 4 mL of the culture was then centrifuged at 10,000 rpm for 90 seconds and then was resuspended in 67 mM phosphate buffer. Final cell density, measured as the optical density at 600 nm (OD₆₀₀), was set to 0.4 (3.0×10⁸ cells/mL) and 1/10 dilution was used for assays.

Assays were prepared in both Teflon and borosilicate scintillation vials (FIG. 1) filled with 1.8 mL assay medium, 200 μL cells, variable DOM concentration (final concentration: 1, 5, 10, 15 and 20 ppm-C) and a concentration of 250 pM Hg^(II) supplied as Hg(NO₃)₂ in 0.2 M HNO₃. For fraction assays, similar volumes of assay media, cells and Hg were used with 1 ppm-C DOC for each fraction to minimize the influence of DOC concentration while maximizing biosensor response. Hg was allowed to equilibrate in the scintillation vials with each treatment for one hour prior to the addition of the cells. Immediately after cell addition, 200 μL of assay solutions were transferred to a 96-well Teflon plate (PFA) and bioluminescence was measured on a multimode plate reader (Tecan F200 Pro) for 4 h (every 5 min). Luminescence of negative controls (no DOM, no Hg) and positive controls (no DOM, 250 pM Hg) were conducted. A control strain (E. coli HMS174 pRB27) that continuously emits light was used to test for variations in light production that were unrelated to the presence of Hg. Two independent bacterial cultures technical triplicates were performed on all concentration regimes as well as all size fractions. Induced luminescence data (expressed as relative light units, RLU) resulting from the presence of intracellular Hg were corrected for the luminescence (RLU) produced by the control strains under the same conditions; as such, bioavailable Hg data are presented as unitless.

(c) FT ICR MS and Statistical Analyses

Ultrahigh resolution mass spectra were obtained using a 7T Bruker SolariX XR FT ICR-MS (Billerica, Mass.) equipped with an electrospray ionization (ESI) ion source and a ParaCell ion cyclotron resonance (ICR) cell. SRFA and PLFA bulk samples and fractions were diluted to 1 ppm-C at pH 2. A methanol to water/sample ratio (40:60) was injected in the FT ICR-MS for blanks and samples, respectively. FT ICR-MS was externally calibrated with a NaTFA tuning mix (Thermo Scientific) prior to sample injection, and internally calibrated with three lock masses (i.e. 248.9603, 656.8848 and 928.8344 m/z). Samples were run in negative ESI with a capillary voltage of 4500V, continuous injection rate of 120 μL/h, and a 2 s ion accumulation time to accumulate 200 scans in adsorption mode²⁶.

Peak assignments were analyzed using Bruker Compass DataAnalysis (v4.2) where elemental constraints for formula assignment were: ¹²C (0-50), ¹H (0-100), ¹⁶O (0-30), ¹⁴N (0-2), ³²S (0-2), ¹³C (0-1)²⁷⁻²⁶, and an error tolerance of ±2 ppm was used. Elemental formulas were exported and an in house Matlab (7.10) script was utilized for van Krevelen diagrams synthesis and percent composition calculations²⁹. Aromaticity index (AI) was calculated based on Koch and Dittmar, 2006³⁰ to determine the average aromaticity of the sample compound³¹ (Equation 1).

$\begin{matrix} {{AI} = \frac{1 + C - O - S - {0.5H}}{C - O - S - N}} & \left( {{Equation}\mspace{14mu} 1} \right) \end{matrix}$

Analysis of variance (ANOVA) tests were conducted in Excel 2011 to test for significance based on biological duplicates. Principal component analyses (PCA) were generated in R (3.22) using the FactoMineR package and multivariable statistics from the software PAST (2.17)³¹ to examine relationships between fraction corn positions.

II. Results and Discussion

(a) Effect of DOC Concentration on Hg Bioavailability

Hg^(II) bioavailability was first tested in the presence of a bulk fraction of SRFA (FIG. 2) and PLFA (FIG. 3) at concentrations ranging from 1 to 20 ppm-C. Hg^(II) uptake increased significantly in the presence of 1 ppm-C SRFA when compared to the DOM-free sample (one-way AVONA, p<0.05) but decreased at [DOC]>5 ppm. In the presence of PLFA, Hg^(II) bioavailability decreased from 1 ppm-C to 20 ppm-C. These data are in line with what was previously observed under equilibrium conditions for which DOM concentration affects Hg uptake^(25,32).

(b) Influence of Molecular Weight of DOM on Hg Bioavailability

The AF4 fractogram revealed a peak maximum at UV 254 nm in the LMW fraction for both SRFA and PLFA (FIG. 4), followed by a decrease in UV response as size ranges increased (FIG. 2). Hg^(II) uptake increased 18.1% and 4.95% in the presence of LMW and MMW from SRFA, respectively (FIG. 5); all PLFA fractions inhibited Hg^(II) uptake, suggesting, while not wishing to be limited by theory, that compounds likely to facilitate Hg uptake are present in SRFA LMW and MMW but absent in PLFA (FIG. 2). In all cases, the HMW fraction was most effective at decreasing Hg^(II) bioavailability leading to a significant (p<0.05 one-way ANOVA) reduction of 18.6% and 37.1% in bioavailable Hg^(II) for SRFA and PLFA when compared to LMW fractions.

(c) Compositional Differences of DOM fractions

The increase in Hg^(II) uptake in the presence of SRFA LMW and MMW fractions, while not wishing to be limited by theory, may be due to the greater H content and lower O content of SRFA compared to the PLFA LMW and MMW fractions (FIGS. 6-11; Tables 1 and 2; FIG. 12). These results suggest, while not wishing to be limited by theory, that hydrogenated DOM preferentially facilitates uptake as opposed to highly oxygenated DOM components³³. Furthermore, the aromaticity index (AI) for LMW and MMW SRFA fractions was lower than for LMW PLFA fractions (FIG. 11). This inverse relationship between AI and bioavailability was observed for both SRFA (r²=0.97) and PLFA (r²=0.99), suggesting that AI may be a useful predictive tool for Hg^(II) bioavailability (FIG. 11)^(2,34). Increasing AI in HMW fractions suggests an increased presence of aromatic phenyl functional groups that are highly polarizable ligands involved in Hg binding³⁵. HMW fractions also had significantly lower C content (p<0.05), H content (p<0.05), higher O content (p<0.01) and largest AI values (p<0.05) indicative of more oxygenated, aromatic DOM than LMW and MMW fractions for both SRFA and PLFA. No significant difference in N and S content was observed within SRFA and PLFA samples (p>0.05; FIGS. 9-10), suggesting, while not wishing to be limited by theory, differences in Hg^(II) bioavailability were not solely driven by N and S content but also by MW and aromaticity characteristics.

Table 1 shows SRFA average atomic ratios and weighted percentage composition for size fractions and unfractionated bulk material based on FT ICR-MS. Table 2 shows PLFA average atomic ratios and weighted percentage composition for size fractions and unfractionated bulk material based on FT ICR-MS. LMW fraction for both SRFA and PLFA have significantly (p<0.05) different % C, % H, and % O compositions than HMW fractions.

TABLE 1 SRFA average atomic ratios and weighted percentage composition. LMW MMW HMW Bulk O/C 0.400647 0.596396 0.641104 0.427424 H/C 1.459999 1.375874 1.215925 1.183298 N/C 0.034593 0.055732 0.079141 0.022384 S/C 0.031918 0.053885 0.111108 0.013898 % C 61.11187 61.13751 52.61252 56.73032 % H 7.529443 7.314263 5.318466 5.155639 % O 25.05265 24.26459 34.33336 34.63011 % N 1.928881 2.185305 2.247054 1.906295 % S 4.396346 5.119319 5.513155 2.160173 Al −0.04537 0.093152 0.243362 0.095427

TABLE 2 PLFA average atomic ratios and weighted percentage composition. LMW MMW HMW Bulk O/C 0.458838 0.644221 0.746329 0.477634 H/C 1.311547 1.268617 1.12748 1.242199 N/C 0.063807 0.027545 0.037222 0.029395 S/C 0.032973 0.039495 0.040227 0.038781 % C 60.27021 56.5063 55.12842 56.58204 % H 6.781622 6.428213 5.172363 5.756577 % O 25.89777 31.02867 33.14295 31.22263 % N 2.629135 1.672934 1.976618 1.879492 % S 4.440544 4.384524 4.601309 5.488923 Al 0.132058 0.035148 0.554714 0.016656 (d) Composition, Size and Hg (II) Bioavailability

To examine the relationships between fraction and compositional differences, principal component analysis (PCA) of percent composition and AI were conducted (FIG. 13). Principal component 1 (PC1) explained 52.6% of the overall variance with negative values indicative of aliphatic material and positive values of enhanced aromatic character whereas principal component 2 (PC2) explained 31.5% of the variance with correlations to N/C and S/C ratios. High H/C ratios indicative of aliphatic material⁹ contributed to the LMW fractions of both SRFA (H/C=1.46) and PLFA (H/C=1.31). While larger MW fractions correlate to AI, these contributions cannot be delineated as they are intrinsically related³⁶.

PLFA fractions displayed a significant (p<0.05) increase in AI from LMW fractions to HMW fractions; however, no change in S content was observed. PC1 eigenvalues showed a strong negative relationship to Hg^(II) bioavailability for both SRFA and PLFA (r²=0.85 and 0.94, respectively) (FIG. 14) suggesting, while not wishing to be limited by theory, a linear relationship between increasing AI and decreasing Hg^(II) bioavailability.

Previous studies have shown that DOM with higher O/C ratios was less bioavailable to microorganisms than DOM exhibiting higher H/C ratios⁹. Together with this new data, this suggests, while not wishing to be limited by theory that Hg^(II) uptake can also be an active process coupled to the use of DOM components as a nutrient source. Furthermore, laboratory studies have shown that LMW S-containing amino acids such as cysteine favor Hg uptake over larger sulfur-containing peptides (e.g. glutathione, GSH)³⁷. Similarly, field experiments^(3,38) suggested that Hg^(II) bioavailability is favored in the presence of small protein-like LMW substances^(2-3, 37-38). In contrast, larger molecular weight fractions favor Hg^(II) stabilization through polydendate interactions and steric shielding of the complex reducing Hg^(II) bioavailability^(7,36-40).

Studies investigating the role of DOM on Hg^(II) bioavailability have revealed the complexity of DOM where organic ligands can both enhance and inhibit Hg Uptake^(2,7,25,32). This duality has also been linked to DOM source and composition. For instance, marine DOM rich in microbial processed material increased Hg bioavailability compared to larger, aromatic terrestrial DOM³⁹. Terrestrial DOM undergoes photochemical and microbial transformations leading to the hydrolysis of large molecules into smaller, hydrogenated fragments and ultimately enhancing microbial carbon consumption^(17,41). The increased uptake of Hg^(II) in the presence of LMW and MMW SRFA suggests, while not wishing to be limited by theory, that the active uptake of Hg^(II) is facilitated by the presence of smaller hydrogenated compounds such as monomeric amino acids and carbohydrates⁴²⁻⁴³.

Aerobic Hg^(II) uptake may, while not wishing to be limited by theory, represent a missing piece in the understanding of how Hg is transferred from the atmosphere to anoxic zones. The present data show that upon Hg^(II) deposition, Hg^(II) bioavailability is enhanced due to its binding to small, hydrogenated biologically labile DOM. Accordingly, while not wishing to be limited by theory, a bioavailable pool of Hg^(II) may temporary be stored in aerobic microbial biomass before settling to anoxic environment where it can be delivered to methylation sites. This temporary storage of Hg^(II) in microbial biomass may limit its interaction with large DOM components that may otherwise limit its transfer to (micro) biota. The present study underscores the need to characterize DOM at a molecular level to evaluate its role on Hg bioavailability; and shows that a multi-pronged approach combining state-of-the-art analytical and microbiology approaches is useful to the study of Hg transformations and key biogeochemical processes.

Example 2: Detection of Mercury-Dissolved Organic Matter Complexes Using High Resolution Mass Spectrometry

Mercury is a toxic metal that has the potential to disrupt natural enzymatic processes and causes cellular stress in its inorganic form (Hg^(II)). Recent anthropomorphic processes have led to increased mercury concentrations in aquatic systems and have prompted further investigation to the current understanding of Hg speciation. Upon Hg^(II) deposition from the atmosphere into aquatic systems, immediate interactions with complex dissolved organic matter (DOM) produced by phytoplankton influence the complexation, mobility and bioavailability of resulting complex²⁵. DOM is a ubiquitous mixture of complex organic molecules that can be operationally defined as material <0.45 μm. Understanding the interactions between Hg and DOM in freshwater environments is useful for understanding mobility and toxicity to aquatic biota. The present study relates to the use of Orbitrap mass spectrometry to detect Hg phytoplankton DOM complexes. While a few known studies have previously utilized HRMS to examine Hg interactions with known ligands, this is the first study that examines Hg-DOM interactions using HRMS. The premise of conducting HRMS on bulk phytoplankton DOM and studying Hg interactions was to validate the fractionation method.

I. Materials and Methods

High resolution mass spectrometry (HRMS) has allowed for the accurate characterization of complex heterogeneous mixtures. The present study utilized HRMS to examine DOM produced by phytoplankton in freshwater settings and how it interacts with environmentally relevant concentrations of Hg (II). By identifying common Hg isotopic shifts, Hg peaks can be identified and corresponding organic ligands and functional groups bound to Hg can be simultaneously identified. Phytoplankton DOM from Chlamydomonas reinhardtii, Chlorella vulgaris and Euglena gracilis was obtained by filtering cultures through a 0.2 μm filter. L-Cysteine (ThermoScientific) was utilized at a 2:1 molar ratio to Hg to detect Hg in the presence of known bound ligands.

2.5×10⁻⁶ M of Hg was added to DOM samples, and diluted with ultrapure MeOH (50:50). The resulting solution was brought to pH 6.8 with NaOH and injected into an Orbitrap Q-Exactive (ThermoFisher) at an injection volume of 50 μl/min and a minimum of 200 scans were acquired in ESI positive mode. Molecular formulas were assigned for peaks with a mass accuracy window ≤2 ppm. Elemental constrains for formula assignment were ¹²C (0-50), ¹H (0-100), ¹⁶O (0-30), ¹⁴N (0-2), ³²S (0-2), ¹³C (0-1), ²⁰²Hg (0-1) using the odd nitrogen rule⁴⁴. Thermo Qualbrowser (Xcalibur 3.0.63) isotope simulation was utilized to reinforce isotopic patterns for observed compounds and their theoretical isotopic shifts. To further reinforce observed isotopic patterns, the computer program “Winnow” was used to detect isotopic patterns of specific Hg containing compounds⁴⁵.

II. Results and Discussion

(a) Mercury-Cysteine Interactions

As can be seen from the results presented in FIG. 15, in a 2:1 molar solution of cysteine and Hg, Hg(Cys)₂ complexes were detected (top) and were comparable to the theoretical isotopic distribution (bottom) with a 94% similarity in a 50:50 MeOH to water matrix.

(b) Phytoplankton-Derived DOM

FIG. 16 shows results relating to phytoplankton derived DOM from Chlorella (left), Chlamydomonas (middle) and Euglena (right) in the absence of Hg. Spectra are a normal distribution with CH₂ Kendrick mass shifts. Weighted average m/z of phytoplankton DOM are 394, 267 and 298, respectively. Inner van Krevelen plots show relatively larger contributions of lipid material in Chlorella, unsaturated hydrocarbons in Chlamydomonas, and proteins produced by Euglena ^(44,28). This was based on O/C and H/C ratios depicted by van Krevelen diagrams. The abundance of low molecular weight material (<900 Da) present in phytoplankton-derived DOM suggests, while not wishing to be limited by theory, highly labile compounds being produced. At environmentally relevant concentrations and ratios of DOM to Hg, a large proportion of Hg was found bound to nitrogen and sulfur containing heteroatoms in phytoplankton DOM. Examining Hg-DOM interactions and both equilibrium and pseudo-equilibrium conditions displayed an overall change in Hg location. Understanding the interactions with phytoplankton-derived DOM upon immediate atmospheric deposition of Hg can aid, for example, in predicting Hg mobility and bioavailability in freshwater systems.

(c) Phytoplankton-Derived DOM Hg Complexes

FIG. 17 shows spectra depicting measured complexes (top) and a comparison to the theoretical isotopic distribution below. For observed spectra, a ±5 ppm difference in observed vs predicted m/z was found. The deconvolution of the peak by Winnow further reinforced the presence of 7 isotopic patterns of Hg. For example, a complex with the formula C₃₇H₆₆OHg (from Chlorella) had a 72% similarity, a complex with the formula C₃₈H₆₂ONHgS₂ (from Chlamydomonas) had a 69% similarity and a complex with the formula C₄H₁₁O₄HgS₂ (from Euglena) had a 62% similarity with the theoretical isotopic distribution.

(d) Hg Bioavailability and Significance

FIG. 18 shows mass spectra and boxes associated with detected organic ligands found complexed to Hg, namely C₃₇H₆₆OHg (from Chlorella; left), C₃₈H₆₂ONHgS₂ (from Chlamydomonas; middle) and C₄H₁₁O₄HgS₂ (from Euglena; right). Other studies can examine how differences in DOM sources may influence Hg uptake and bioavailability (see, e.g. Example 1). Based on comparison to structures in ChemSpider, proposed structures for these formulae are, shown, respectively, in Scheme 1:

III. Summary

High resolution mass spectrometry can be utilized to identify organic ligands bound to Hg. Based on bioassays results, size of DOM is an important variable when determining variability. Therefore, the relative abundance and m/z of the HRMS Hg—DOM complexes detected can be used to predict the bioavailability. The subsequent fractionation of the Hg-DOM complexes can be facilitated. While previous methods provide minimal speciation information, the present methods can provide elemental and structural information of organic ligands produced by phytoplankton for Hg binding.

Example 3: Fractionated LMW Compounds for Mobilization of Mercury

Asymmetrical flow field-flow fractionation (AF4) was used to separate dissolved organic matter from Suwannee River Fulvic Acid (SRFA), Chlorella vulgaris, Chlamydomonas reinhardtii, and Euglena gracilis into three separate fractions based molecular weights (FIG. 19). Low molecular weight (LMW: 300-900 Da), medium molecular weight (MMW: 900-1800 Da) and high molecular weight (HMW: 1800-3500 Da) fractions were collected and exposed to 250 pM of Hg(NO₃)₂. Bar graph results are shown in (FIG. 20). These findings show, for example, fractionated LMW organic compounds may be utilized for controlling the mobilization of mercury in contaminated bodies of water.

Example 4: Identification of Mercury-Binding LMW Compounds: Molecular Interactions Between Phytoplankton Based DOM and Mercury Revealed by High Resolution Mass Spectrometry

The composition of phytoplankton DOM and its interactions with Hg are fundamental steps to understand how inorganic Hg is internalized by methylating organisms. High resolution mass spectrometry (HRMS) has been used to provide compound level information for international humic society standard (IHSS) standards, algae and DOM. The objectives of this work are, for example, to: (1) assess phytoplankton DOM-Hg interactions using HRMS and (2) investigate structural properties of Hg binding DOM during different light cycles. The sensitivity and resolution of Orbitrap mass spectrometry allows for the detection of DOM-Hg complexes.

I. Materials and Methods

(a) Algal Growth and DOC Concentrations

Euglena gracilis Klebs were obtained from Boreal Laboratory Supplies Ltd (St. Catharines, ON, Canada). Euglena gracilis was grown under 16:8 h light to dark cycle using bold basal media (BBM) at pH 5.65. Cells were harvested at approximately 1.0×10⁶ cells/mL for DOM analyses. Laboratory grown cultures of Chlamydomonas reinhardtii, Chlorella vulgaris and Scenedesmus obliquus were obtained from the Canadian Phycological Culture Center (CPCC) in Waterloo, Ontario and grown using a high salt media (HSM) for Chlamydomonas and a BBM for Chlorella and Scenedesmus. Growth conditions included photoperiods of standard and high light regimes (16:8 h and 20:4 h light to dark, respectively) at a fixed light intensity of 90-100 μmol photons m⁻¹ s⁻¹ and a fixed temperature of 21° C. Cultures were harvested at mid exponential growth phase where the cell density was 1×10⁶ cells/mL and filtered through a pre-combusted 0.7 μm glass fiber filter (GF/F Whatman) into acid washed and pre-combusted glassware. Biological duplicates of phytoplankton-derived DOM were collected at both light regimes. Filtered phytoplankton-derived DOC concentrations were measured using a total organic carbon (TOC) analyzer and fixed to 1 mg C. L⁻¹ for further analyses (Table 3).

TABLE 3 DOC Concentrations (mg/L) for Chlorella, Chlamdyomonas and Scenedesmus exudates at different light regime growth conditions of 16:8 h and 20:4 h (light:dark; n = 2). 16:8 h 20:4 h Chlorella 7.3 ± 1.2 9.6 ± 0.9 Chlamydomonas 6.1 ± 0.8 10.3 ± 1.5  Scenedesmus 3.7 ± 0.4 5.2 ± 0.6 (b) qBBr Titration

Fresh stock solution of 0.001 M qBBr (SigmaAldrich) was prepared daily in an amber glass bottle covered in aluminum foil. A series of qBBr standard addition solutions was prepared by mixing 5 mL of DOM samples with different volumes of qBBr (0, 25, 50, 100, 250, 400, 500, 600, 750, 900 μL), resulting in corresponding final qBBR concentrations of 0, 4.98, 9.90. 19.61, 47.62, 74.07, 90.91, 107.14, 130.43, 152.54 μM. Mixtures were covered with aluminum foil and mixed for an hour at room temperature. qBBr-equivalent thiol concentration was determined with this standard addition using a Fluoromax4 spectrophotometer (Horiba Jobin Yvon) equipped with a 1 cm quartz cuvette. The excitation wavelength of 380 nm was used and the sample emission was monitored from 400 to 500 nm. Maximum emission at 470 nm (A₄₇₀) was measured after correcting for qBBr emission background. To obtain background fluorescence of qBBr solution, a series of solutions were examined similarly, with milliQ in place of DOM samples. As the qBBr tag binds to thiols in a 1:1 molar ratio, the level of qBBr saturation in samples corresponded to thiol concentration. Total thiol concentration was determined using non-linear piece-wise regression (SigmaPlot, v10) (0.97<R²<0.99; p<0.05)²¹.

(c) High Resolution Mass Spectrometry

The molecular composition of phytoplankton-derived DOM was determined using the Orbitrap Q Exactive (Thermo Fisher Scientific, Bremen, Germany) equipped with a heated electrospray ionization (HESI) source. Prior to injection, samples were diluted to a 50:50 sample to MeOH ratio with ultrapure MeOH (99.9% HPLC grade; Sigma Aldrich) and the pH adjusted to 6.8 with ultrapure NaOH (Sigma Aldrich). Positive ionization mode [M+H]⁺ was utilized and samples were injected at a consistent flow rate of 50 μL/minute with an electrospray needle voltage of 4 kV and a heated capillary temperature of 300° C. Positive ionization for ESI was utilized as no Hg containing compounds were detected in negative mode by Chen et al., 2017 when using high resolution mass spectrometry while positive ESI has been utilized when examining bacterial derived DOM⁵³. A resolving power of 140,000 (full width half maximum @ m/z 200) was found and sodium trifluoroacetate (NaTFA, Sigma-Aldrich 98%) was added as an internal standard in each sample to ensure exact mass accuracy between a mass range of 200-1000 m/z. Samples were acquired for a minimum of 5 minutes to allow for 200 scans to be co-added in the data post analysis stage of the Thermo Xcalibur Qual Browser (3.0.63) software. Background subtractions were conducted for phytoplankton growth media and MeOH: ultrapure mixtures prior to formula assignment. Elemental constraints for formula assignment were: ¹²C (0-50), ¹H (0-100), ¹⁶O (0-30), ¹⁴N (0-2), ³²S (0-2), ¹³C (0-1), ³⁴S (0-1) and ²³Na (0-1) using the odd nitrogen rule. Molecular formulas were validated based on homologous series Kendrick mass defect shifts (CH₂), carbon and sulfur isotopes (¹³C and ³⁴S) to formulas where the signal to noise ratio was ≥4 within ±2 ppm exact mass error (FIGS. 21 and 22, respectively)^(28, 49). Molecular formulae with a modified aromaticity index (AI_(mod)) >0.67 were omitted from further analyses³⁰. A MatLab script was used to determine the number of high resolution mass spectrometry compound classes based on van Krevelen diagrams. Briefly, lipid material can be found (0.01≤O/C≤0.1; 1.5≤H/C≤2.0), unsaturated hydrocarbons (0.01≤O/C≤0.1; 0.75≤H/C≤1.5), condensed aromatic structures (0.01≤O/C≤0.65; 0.25≤H/C≤0.75), protein (0.1≤O/C≤0.65; 1.5≤H/C≤2.3; N≥1), lignin (0.1≤O/C≤0.65; 0.75≤H/C≤1.5) with no heteroatoms (only CHO), tannins (0.65≤O/C≤0.85); (0.75≤H/C≤1.5) and carbohydrate (0.65≤O/C≤1.0; 1.5≤H/C≤2.5)^(28,29,49). Intensity weighted averages of O/C_(wa), H/C_(wa), S/C_(wa), % C_(wa), % H_(wa), % O_(wa), % N_(wa), % S_(wa), m/z_(wa), modified aromaticity index (AI_(mod)) and the nominal oxidation state of carbon (NOSC) were also calculated for phytoplankton derived DOM at both light regimes⁵⁰⁻⁵².

(d) Mercury Detection

Hg solutions were prepared by mixing 2.5×10⁻⁶ mol L⁻¹ of Hg (NO₃) (AAS grade) and 1 ppm of organic ligand (i.e. phytoplankton DOM or L-Cysteine) and kept in the dark for at least 24 h prior to analysis. A comparable Hg concentration was utilized in a previous study examining Hg-sulfur interactions using Orbitrap mass spectrometry⁴⁷. The pH solution was fixed to pH 6.8 with ultrapure NaOH. After the addition of Hg to L-Cysteine (SigmaAldrich) or DOM, samples were analyzed on the Orbitrap mass spectrometer after 24 hours of contact time. To detect Hg containing compounds, ²⁰²Hg and ²⁰⁰Hg isotopes were added to the elemental constraints for formula assignment, similar to previous ESI high resolution mass spectrometry Hg studies⁴⁶. The software Winnow⁴⁵ was used to detect 7 isotopologues of Hg (¹⁹⁶Hg, ¹⁹⁸Hg, ²⁰⁰Hg, ²⁰¹ Hg, ²⁰²Hg and ²⁰⁴Hg). Only the peaks with a Winnow score of greater than 70% were validated based on ²⁰²Hg and ²⁰⁰Hg natural Hg isotope abundances to confidently identify Hg containing DOM compounds using Xcalibur Isotope simulation (3.0.63). To compare structural differences between Hg binding DOM, a two-way hierarchal cluster analyses and non-parametric Spearman's correlations were conducted based on weighted averages of O/C, H/C, N/C, S/C atomic ratios, elemental percentage compositions for % C, % H, % N, % O, % S and AI_(mod), NOSC and m/z at 16:8 h and 20:4 h cycles using JMP (version 11). Clusters were based on Bray-Curtis similarity measure at a 95% confidence interval. A one-way analysis of variance (ANOVA) was also conducted for biological duplicates to compare weighted averages, changes in m/z distribution and compounds class differences.

(e) Putative Molecule Identification

In order to identify putative ligand-Hg complexes, organic ligands complexed to Hg were further compared to a database of known bacterial siderophores, ligands from the Kyoto Encyclopedia of Genes and Genomes (KEGG) database and Metlin Metabolite database based on m/z comparisons with an error ≤2 ppm and isotope pattern comparisons^(45,54-58). A similar approach has been conducted for metabolomics work incorporating FT ICR-MS to allow for a high-throughput detection of metabolites with a high degree of accuracy⁵⁹. The ¹⁴N range was increased from <3 to <7 when comparing structures to databases to allow for the potential exact mass identifications of siderophores and ligands. The structure of these compounds may, for example, be confirmed by conducting tandem MS/MS analyses. Theoretical isotopic distributions of these putative isomers were examined to allow for both exact mass and isotopic confirmation of Hg-binding compounds.

II. Results and Discussion

(a) Changes in DOM Composition with Increased Light Exposure

FIGS. 23-26 show changes in DOM composition with increased light exposure from Chlorella in the absence (FIGS. 23 and 25) and presence (FIGS. 24 and 26) of Hg. FIGS. 27-30 show changes in DOM composition with increased light exposure from Chlamydomonas in the absence (FIGS. 27 and 29) and presence (FIGS. 28 and 30) of Hg. FIGS. 31-34 show changes in DOM composition with increased light exposure from Scenedesmus in the absence (FIGS. 31 and 33) and presence (FIGS. 32 and 34) of Hg. A total of 482-1541 mass peaks was assigned between these three taxa during the two photoperiods. The mass peaks were mainly made up of singly charged peaks (FIGS. 23-34) and CH₂ homologous series validated shifts (FIGS. 23-34; inner graphs). At a 16:8 h light:dark photoperiod duration, each of these three phytoplankton taxa exhibited compositional differences in produced DOM. Firstly, Chlorella displayed a lower average m/z_(wa) than Scenedesmus and Chlamydomonas (643 vs 731 and 676; FIG. 35; second plot from right on the top row). Chlorella displayed larger H/C_(wa), N/C_(wa) and S/C_(wa) when compared to other taxa suggesting while not wishing to be limited by theory the release of smaller aliphatic sulfur containing proteins (FIG. 35; 2-4 plots from the left on the top row)⁶⁰ . Chlamydomonas DOM had the largest % C_(w), (70.8%), followed by Scenedesmus (68.7%) and Chlorella (67.7%) (FIG. 35; far left plot on bottom row). After increasing the photoperiod duration to 20 h, the average elemental ratios of phytoplankton DOM shifted to higher H/C_(wa) and lower AI_(mod) for all phytoplankton, consistent with more aliphatic, hydrogenated material being secreted (FIG. 35; second plot from left on top row and far right plot on top row, respectively). % N_(wa) did not significantly change for Chlorella (2.89±0.08% vs 2.32±0.14%), Scenedesmus (2.08±0.13% vs 1.98±0.02%) and Chlamydomonas derived DOM (1.79±0.07% vs 1.97±0.28%) (FIG. 35; third plot from left on bottom row). The % S significantly increased for Chlorella (3.33±0.06% vs 3.81±0.17%) and Chlamydomonas (3.37±0.02% vs 4.05±0.22%) whereas no significant change in % S was found for Scenedesmus (3.21±0.07% vs 3.45±0.11%; ANOVA p>0.05). qBBr titrations revealed significant increases in qBBr active thiol concentrations for Chlorella and Chlamdyomonas, (ANOVA; p<0.05) but these trends were not observed for Scenedesmus, comparable to HRMS results (Table 4). NOSC_(wa) values increased for all phytoplankton DOM suggesting, while not wishing to be limited by theory, a shift from nonpolar to more polar compounds as light durations increased (FIG. 35; far right plot on bottom row). Although photo-oxidative stress was not explicitly measured, a higher degree in photorespiration caused by photo-oxidative stress has, while not wishing to be limited by theory, been proposed as a mechanism of increased carbon loss in phytoplankton, congruent with the increasing DOC concentrations measured in higher light cultures (Table 3)⁶¹.

TABLE 4 qBBr-equivalent thiol concentrations (μmol/g_(algae)) of phytoplankton exudates grown at different light regime growth conditions of 16:8 h and 20:4 h (light:dark, n = 2). 16:8 h 20:4 h Chlorella 32.39 ± 0.406 1846 ± 594.3 Chlamydomonas 856.0 ± 168.7 4225 ± 1379  Scenedesmus  2201 ± 595.1 2127 ± 728.8

Van Krevelen diagrams (FIGS. 36-38) indicated that the higher light duration (bottom) impacted the compound classes of DOM excreted by phytoplankton in comparison to the standard light duration (top). Significant increases in protein (45.3%-57.5%), lipids (21.4-26.3%) and unsaturated hydrocarbons (3.85-10.1%) (ANOVA; p<0.05) compound groups were observed across all phytoplankton taxa, consistent with the abundance of amino acids, fatty acids and monosaccharides released by algae (FIG. 39)^(21,60-62). Although making up a very small proportion of compounds, the aromatic structures decreased from 0.45% to 0.06% in Chlamydomonas and 0.51% to 0.11% for Scenedesmus with increasing light exposure, while not wishing to be limited by theory, likely due to photodegradation of the π structures⁶³ (FIG. 39). The lipid and protein abundances increased by 14-15% in Chlorella, whereas only lipid DOM increased for Scenedesmus (17%; ANOVA p<0.05). While Chlamydomonas, Chlorella and Scenedesmus have been known to have high intracellular proteins and lipid content⁶⁴⁻⁶⁶, the higher light duration may not have been enough to induce a significant change in the relative abundance of proteins and lipids released by Scenedesmus, while not wishing to be limited by theory, likely due to its high tolerance to prolonged light exposure⁶⁷. Many sulfur containing amino acids and proteins such as cysteine and GSH have been shown to increase in concentration when marine phytoplankton are exposed to increased light⁶⁸; however, Scenedesmus may be resistant to the light cycles used. Scenedesmus was the only organism to display a significant decrease in unsaturated hydrocarbons (10.1%-6.28%; ANOVA p<0.05) with higher light exposure (FIG. 39; third plot from left on the top row). While not wishing to be limited by theory, higher light exposures can cause the conversion of unsaturated odd chain-hydrocarbons into smaller saturated lipids in algae⁶⁹. Carbohydrate content did significantly increase with light exposure for Chlamydomonas and Scenedesmus (p<0.05), while not wishing to be limited by theory, likely due to the degradation of phytoplankton cell walls during periods of oxidative stress induced by light (FIG. 39; third plot from the right on the top row and third plot from the right on the bottom row, respectively)⁷⁰.

Upon increasing photoperiod duration, a 51% increase in lignin (11.5%-7.61%; ANOVA p<0.05), and a 14% decrease in protein material (45.3-52.2%; ANOVA p<0.05) DOM were observed in Chlorella DOM exudates (FIG. 39; first and second plots from the left on the top and bottom rows, respectively); no other DOM compound class showed significant changes for Chlorella at higher light regimes (FIGS. 23-34 and 39). While lignin is known to provide cell wall support⁷¹, active secretion of these compounds has been reported as a possible source of a non-vascular plant derived lignin source⁷². Proteinaceous material in the form of amino acids and larger peptides as well as cyclic carbohydrates serve as advantageous components of the total dissolved organic nitrogen (DON) and are the predominant compound class accounting for more than 50% of the material released by phytoplankton^(61,73,74), congruent with high protein abundances found in this study (FIG. 39 second plot from the left on the top and bottom rows). Chlamydomonas did not vary significantly for the majority of compound classes (p>0.05) apart from a significant decrease in aromatic species at higher light exposure (0.51 vs 0.10%; p<0.05). While DOM released varied based on phytoplankton taxa, a higher light exposure led to an overall increase in smaller molecules that are generally more aliphatic and polar in structure. This suggests, while not wishing to be limited by theory, a shift towards a more protein- and lipid-rich environment as phytoplankton blooms progress in sub-Arctic environments.

(b) Hg-Cysteine

Hg complexation was observed in the presence of model ligands, i.e. cysteine where the exact mass was less than ±5 ppm for all Hg isotopes in a simple MeOH: H₂O matrix⁴⁶. Among the 6 Hg-containing formulas, ²⁰²HgC₆H₁₃N₂O₄S₂ ⁺ was identified in the Hg-cysteine sample (1:2 molar ratio) in positive mode (FIG. 40; top). The overall distribution of Hg isotopes was consistent with the theoretical isotopic distribution natural abundances⁴⁶ (FIG. 4O; bottom). The experimentally derived spectra revealed the ²⁰²Hg and ²⁰⁰Hg isotopes differing by −2.25 ppm and −2.26 ppm from the theoretical distribution, respectively as most abundant peaks. The peak intensity ratio between ²⁰²Hg and ²⁰⁰Hg was 0.81:1 for the detected Hg-Cys complex, comparable to the natural isotopic ratio (0.77:1)⁴⁶. While the exact mass of Hg isotopes in other studies incorporating a 15T Fourier transform ion cyclotron mass spectrometry (FT ICR MS) achieved ±1 ppm, these results show that Hg isotopes can be usefully identified using Orbitrap mass spectrometry in complex mixtures⁷⁵. While FT ICR-MS has become the stand alone method of choice for DOM characterization, Orbitrap mass spectrometry can be utilized for the accurate determination of molecular composition of DOM while providing confident information about dominant Hg isotopes⁷⁵.

(c) Changes in Hg Ligand Composition with Light

Entire spectra of phytoplankton-derived DOM were similar before and after Hg addition suggesting, while not limited by theory, limited ion suppression during ESI Orbitrap HRMS (FIGS. 23-34). A total of 44, 61 and 52 Hg-DOM complexes were detected at the 16:8 h light regime and increased to 85, 121 and 53 in the 20 h light cultures of Chlorella, Chlamydomonas, and Scenedesmus, respectively. Detected Hg-DOM complexes accounted for approximately 1.6-2.6% of the total assigned peaks across all samples. The addition of Hg to phytoplankton DOM allowed for the identification of Hg isotopologues while retaining similar peaks in the metal free sample (FIG. 41). Experimentally detected elemental formulas of [²⁰² HgC³⁵H⁶⁰O⁷N²S]⁺, [²⁰² HgC₃₉H₈₂O₆NS₂]⁺ and [²⁰²HgC₃₇H₆₄O₆N]⁺ were validated based on exact mass and theoretical Hg isotopic distribution in Chlorella, Chlamydomonas and Scenedesmus, respectively (FIG. 42; second from top, third from bottom, bottom, respectively). While ²⁰⁰Hg and ²⁰²Hg isotopes were checked for the isotopic confirmation of Hg, the presence of lower abundance Hg isotopes (i.e. ¹⁹⁶Hg, ¹⁹⁸Hg, ²⁰¹Hg, and ²⁰⁴Hg) was also observed (FIG. 42) but at much lower relative intensities compared to a 15T FT ICR-MS⁴⁶.

At the 16:8 h light cycle, most DOM complexed to Hg were CHO in composition for Chlorella (15 formulas), Chlamydomonas (14 formulas) and Scenedesmus (10 formulas) (FIG. 43, top). The importance of Hg:DOM ratios when determining binding constants for Hg and DOM ligands has been demonstrated⁷⁶ and in natural conditions, Hg to DOM ratios are approximately 5 nM Hg/mg DOM where speciation is largely defined by reduced thiols functional groups⁷⁶. In this study, Hg DOM ratios are 250 nM Hg/mg of DOM, suggesting, while not wishing to be limited by theory, that many Hg binding sites are dominated by oxygen functional groups^(46, 61, 76). However, at higher light regimes 20:4 (FIG. 43, bottom), compound classes containing both oxygen and nitrogen atoms composed of the vast majority of Hg bound DOM for Chlamydomonas and Scenedesmus due to the enhanced production and abundance of CHON coupled with high Hg:DOM ratios^(61, 74). Sulfur heteroatoms are an important variable to consider at lower Hg:DOM ratios and sulfur containing DOM content varied between taxa (5.15-5.89%). A total of eight CHOS₂ formulas produced by Chlamydomonas were bound to Hg, making it the most abundant sulfur containing class that binds to Hg at 16:8 h photoperiod duration (FIG. 43, top). Detected Hg binding DOM classes that contain at least one sulfur atom (CHOS, CHOS₂) increased from 9 to 54, 17 to 21 for Chlorella and Chlamydomonas, respectively but no significant change was observed for Scenedesmus (27 to 25 16:8-20:4 h), consistent with the overall trends in % S_(wa) at higher light regimes (FIG. 35, second plot from right on bottom row). These results highlight that the increased light exposure prompted a 2.13-fold increase in the number of S-containing ligands Hg in Chlorella vulgaris mainly in the form of Hg bound CHONS compounds.

The proportion of Hg binding DOM also changed from 16 to 20 h light exposure. The most notable difference was the reduction in Hg bound CHO species in all taxa (15 to 11 molecules for Chlorella, 14 to 11 molecules for Chlamydomonas and 10 to 6 molecules for Scenedesmus) (FIG. 43, bottom). Increasing the light duration prompted a spike in CHONS compounds produced by Chlorella from 3 to 27 of all compounds complexed to Hg, consistent with the overall increase in protein material at higher light intensities (FIG. 39, second plot from left on top and bottom rows). Detected CHOS compounds complexed to Hg increased with light exposure across all taxa (3 to 10 for Chlorella, 3 to 7 for Chlamydomonas and 3 to 5 for Scenedesmus).

(d) Structural Properties of Hg Binding DOM

To assess how structural properties of Hg binding DOM vary between taxa and with light exposure, a two-way hierarchal cluster analysis with correlation heatmaps was conducted (FIGS. 44-45). Three clusters were found for each light regime based on 95% Bray-Curtis similarity measure (FIGS. 44-45). Group 1 included 70% of the molecular formula compound classes at the 16:8 h light regime, mainly from Scenedesmus and Chlorella, linked by similarities between % N_(wa), N/C_(wa), m/z_(wa), % H_(wa), H/C_(wa) and % C_(wa) of secreted Hg binding DOM. Chlamydomonas CHOS, CHOS₂, CHO and CHON₂S Hg binding DOM compounds were clustered in Group 2, largely due to the strong influence of % O_(wa), O/C_(wa), NOSC_(wa) and AI_(mod). Group 3 included Chlorella and Scenedesmus CHOS₂ compounds, predominantly influenced by high % S_(wa), S/C_(wa), O/C_(wa) and NOSC_(wa) . Chlorella and Scenedesmus produced smaller, N-rich and polar Hg binding ligands when compared to the larger more aromatic and oxygenated DOM released by Chlamydomonas. While changes in photoperiod duration yielded changes in the number and proportion of Hg-binding molecules, the overall structural properties AI_(mod), % C_(wa), % H_(wa), % O_(wa)) of Hg-binding DOM did not significantly change. A significant change (p<0.05) in the proportion of CHO and CHONS at 16:8 to 20:4 was observed, but the overall structural properties of Hg binding DOM (AI_(mod), O/C_(wa), N/C_(wa)) did not significantly change between light regimes.

Higher light exposure increased % S_(wa) and the number of Hg-sulfur interactions increased, the structural properties of the sulfur containing molecules did not significantly vary. The influence of phytoplankton taxa was more important on Hg binding DOM than the compositional changes caused by higher light exposure. As photoperiods increased, a shift from Hg complexed by CHO to CHONS, CHON and CHON₂S ligands were observed indicating a shift from Hg binding to aromatic DOM towards Hg binding to protein-rich DOM^(41,77). With the availability of more sulfhydryl binding sites at increased photoperiods, a shift from amine and carboxyl functional groups to thiols may be observed, even at higher DOM:Hg ratios (Table 4)⁷⁸. Structural properties of released DOM are largely governed by phytoplankton species and while assessing present thiol and sulfhydryl binding sites allows for predicting of Hg complexation, the structure of the side chain attached to the sulfur containing group has advantageous implications for the bioavailability of the complex^(78,79). While certain phytoplankton DOM abundant in low molecular weight thiols may act as a shuttle for Hg to bacteria, larger sinking phytoplankton DOM may facilitate Hg mobility to larger colloidal organic matter fractions where Hg methylation also occurs^(41, 79, 80).

(e) Identification of Hg-Phytoplankton Derived DOM Complexes

The present research incorporates Orbitrap high resolution mass spectrometry to allow for the confident identification of Hg-phytoplankton derived DOM complexes. The low molecular weight DOM were identified to include at least desferrioxamine, cyclic trichrisobactin, carboxymycobactin monohydrate, exochelin from Chlorella; ferrioxamine from Chlamydomonas; desferrioxamine, desferrioxamine monohydrate, vibrioferrin and acinetoferrin from Scenedesmus; and siderochelin A, benarthin, chrysobactin, dihydroxybenzoic acid, rhizobactin, and schizokinen from Euglena. Table 5 shows the identities of LMW DOM compounds from Chlorella, Chlamydomonas, Scenedesmus and Euglena gracilis.

TABLE 5 Complexes identified in Chlorella (20:4); Scenedesmus (16:8) and (20:4); Chlamydomonas (16:8) and Euglena. Mass Details Structure/Name Chlorella (20:4) Theo Mass [H+]: 922.3844396 Observed: 922.38139 Error ppm: −3.306 Intensity: 32460.6 Relative: 0.34 Resolution: 55354.92 Formula: C31H57N7O12Hg

Theo Mass [H+]: 980.3436366 Observed: 980.34074 Error ppm: −2.955 Intensity: 25337.9 Relative: 0.26 Resolution: 53989.57 Formula: C34H51N9O12Hg

Theo Mass [H+]: 978.3419056 Observed: 978.34468 Error ppm: 2.8358 Intensity: 22118.2 Relative: 0.23 Resolution: 57523.44 Formula: C37H54N5O13Hg

Theo Mass [H+]: 912.3385516 Observed: 912.34205 Error ppm: 3.8345 Intensity: 29098.5 Relative: 0.3 Resolution: 59399.79 Formula: C27H51N9O13Hg

Details Structure/Name Scenedesmus (16:8) Theo Mass [H+]: 870.3571616 Observed: 870.35989 Error ppm: 3.1348 Intensity: 74765.4 Relative: 0.13 Resolution: 65932.81 Formula: C32H53N5O10Hg

Theo Mass [H+]: 918.3895246 Observed: 918.39265 Error ppm: 3.40312 Intensity: 102490.5 Relative: 0.18 Resolution: 64258.09 Formula: C32H57N7O11Hg

Scenedesmus (20:4) Theo Mass [H+]: 633.0649906 Observed: 633.06433 Error ppm: −1.0435 Intensity: 44317.8 Relative: 0.1 Resolution: 71400.33 Formula: C16H18N2O12Hg

Theo Mass [H+]: 870.3571616 Observed: 870.35982 Error ppm: 3.05437 Intensity: 58580.8 Relative: 0.13 Resolution: 63902.28 Formula: C32H53N5O10Hg

Theo Mass [H+]: 918.3895246 Observed: 918.39269 Error ppm: 3.44668 Intensity: 56188.2 Relative: 0.13 Resolution: 60213.31 Formula: C32H57N7O11Hg

Chlamydomonas (16:8) Theo Mass [H+]: 952.3864506 Observed: 952.38897 Error ppm: 2.645 Intensity: 20786.4 Relative: 0.15 Resolution: 56545.67 Formula: C36H57N6O11Hg

Euglena gracilis Hg Binding DOM Theo. Mass: 436.0653 Hg: 436.0658 No Hg: 234.1044 Intensity: 31598.2 Relative: 0.13 Delta (ppm): 1.05 RBE: 6.5 Composition: C12H14N2O3Hg Composition-Hg: C12H14N2O3 Theo Mass no Hg: 234.1001 Error (ppm): 4.343

Theo. Mass: 614.1977 Hg: 613.1474 No Hg: 411.1768 Intensity: 69622.3 Relative: 0.3 Delta (ppm): −0.5 RBE: 14.5 Composition: C17H25N5O7Hg Composition-Hg: C17H25N5O7 Theo Mass no Hg: 411.1748 Error (ppm): 1.983

Theo. Mass: 571.1191 Hg: 571.119 No Hg: 369.1546 Intensity: 37318.3 Relative: 0.16 Delta (ppm): −0.25 RBE: 15.5 Composition: C16H23N3O7Hg Composition-Hg: C16H23N3O7 Theo Mass no Hg: 369.153 Error (ppm): 1.602

Theo. Mass: 355.9994 Hg: 355.999 No Hg: 154.02661 Intensity: 52415.8 Relative: 0.22 Delta (ppm): −1.12 RBE: 9.5 Composition: C7H6O4Hg Composition-Hg: C7H6O4 Theo Mass no Hg: 154.0264 Error (ppm): 0.21

Theo. Mass: 580.2134 Hg: 579.1473 No Hg: 377.17728 Intensity: 102489.9 Relative: 0.44 Delta (ppm): −0.18 RBE: 10.5 Composition: C15H27N3O8Hg Composition-Hg: C15H27N3O8

Theo Mass no Hg: 377.1791 Error (ppm): −1.817 Theo. Mass: 621.9708 Hg: 622.1507 No Hg: 420.18008 Intensity: 24838.9 Relative: 0.11 Delta (ppm): −0.18 RBE: 4.5 Composition: C16H28N4O9Hg Composition-Hg: C16H28N4O9

Theo Mass no Hg: 420.1849 Error (ppm): −4.817

By incorporating a top-down shotgun based approach, previously devised bacterial siderophores, KEGG ligand databases, and Metlin were searched to identify putative Hg binding metabolites present in phytoplankton exudates. While bacterial siderophores are traditionally produced to sequester iron required for metal homeostasis, these ligands have been known to interact with a wide range of soft metals, including Hg⁸¹. Based on siderophore databases⁵⁶, and comparing experimental and theoretical isotopic patterns, empirical formulas of seven potential Hg binding siderophores were identified (FIGS. 46-51). The putative compounds included desferrioxamine, cyclic trichrisobactin, carboxymycobactins, and exochelin in Chlorella, and acinetoferrin and desferrioxamine in Scenedesmus. While Hg-DOM complexes were detected for Chlamydomonas, none of these detected compounds were found in the siderophore database⁵⁶.

Using the KEGG ligand database, additional putative ligands were found based on exact mass and molecular composition (Table 6).

TABLE 6 KEGG Database Matches-Phytoplankton Exudates. Molecular Phytoplankton Formula Exudate Sample (m/z) Structure/Name Chlorella 16:8 C9H9O2N (163.0633)

Chlorella 16:8 C12H15O2N (205.1103)

Chlorella 16:8 C18H31O (264.244693)

Chlorella 20:4 C11H19O9NS (373.0501)

Chlorella 20:4 C19H35O4N3S (401.2348)

Chlamydomonas 20:4 C22H47O5N (405.3454)

At lower light regimes, matches with molecules C₉H₉O₂N and C₁₂H₁₅O₂N with possible structures resembling 3-methyldioxyindole an indication of tryptophan metabolism and degradation⁸⁰ and N-acetyl-leucyl-methionine, a sulfur based amino acid protease inhibitor⁸² in Chlorella exudates. Possible isomers of aminopentol (C₂₂H₄₇O₅N), a hydrolysis product of fungal mycotoxins commonly found on corn and other lipid-rich nutrient sources was found complexed to Hg in Chlamydomonas exudates at higher light regimes⁸³.

Examining phytoplankton exudates using Metlin yielded additional compounds of microorganism origin (Table 7). For example, C₇H₁₄O₃ found in Chlorella cultures at higher light regimes produced a potential isomer of a heptanoic acid, an oily carboxylic acid commonly found in algae complexed to Hg⁸⁴. Furthermore, C₄₂H₈₁NO₃ found at Chlamydomonas during higher light regimes is a potential isomer of ceramide, a lipid assisting motile algae to swim towards light⁸⁵. Finally, Scenedesmus at lower light durations revealed C₃₈H₆₇N₂O₄S, a possible isomer of tetradecane that possesses antimicrobial properties, complexing with Hg⁸⁶.

TABLE 7 Hg binding algal-derived ligands. Relative m/z Abun- (Composition) Name and Reference Proposed Structure dance Chlorella16:8 541.461563 (C36H61O3) Momordicilin Kumar et al 2015⁸⁷

0.67 379.129713 (C15H25O8NS) Sulfanilamide Singh 1975⁸⁸

0.27 551.503263 (C35H67O4) Dihydroxypentatri- aconta-2,4-dienoic acid Laboratory techniques in Biochemistry and Molecular Biology. Chapter 1 Lipids⁸⁹

0.23 Chlorella 20:4 155.080733 (C19H32O6N6) Ala Thr Leu His Peptide chain of 4 amino acids

2.69 147.101563 (C7H14O3) 2-Hydroxyheptanoic acid Everall and Lees 1997⁹⁰

1.45 145.085883 (C7H12O3) (E)-penta-1,3-dien-2- ol Bagwell et al 2014⁹¹

0.87 629.513923 (C40H68O5) Diglyceride Waxy lipid composed of two fatty chains Choi et al 1987⁹²

0.35 471.367853 (C27H50O6) Glycerol triaprylate U.S. Pat. No. 7,220,417 B2

0.34 Chlamydomonas 16:8 377.086613 (C18H17O9) 5,7,3′,4′- Tetrahydroxy-3,6,5′- trimethoxyflavone Rabesa and Voirin 1980⁹³

0.18 423.419743 (C28H55O2) 9-Octadecenoic acid Abdel-Aal et al. 2015⁹⁴

0.29 Chlamydomonas 20:4 769.085773 (C33H22N4O17) 1,2,3,4-tetrakis-o-(4- nitrobenzoyl) pentopyranose Vestola et al 2014⁹⁵

1.16 648.628843 (C42H81NO3) Ceramide Michaelson et al 2010⁹⁶

0.69 365.011463 (C11H12N2O8 S2) Cefsulodin monobactam Rossolini and Docquier 2006⁹⁷

0.64 345.009093 (C14H7N2O8) 2,7,9- Tricarboxypyrrolo(2, 3-f)quinoline-4-ol-5- one Prince and Gallant 1983⁹⁸

0.58 Scenedesmus 16:8 616.475733 (C38H67N2O4S) Tetradecane-1 Yamamoto et al 2014⁹⁹

0.30 Scenedesmus 20:4 619.478213 (C34H66O9) 1-(O-alpha-D- glucopyranosyl)-3-keto- (1,25R,27R)- octacosanetriol Bauersachs 2010 (Thesis)¹⁰⁰

0.25 661.464353 (C42H58N6O2) 2,4-Bis[4,5- bis(pentylamino)isoquinolin- 1-yl]cyclobutane-1,3- dione US 2008/0194732 A1

0.21 (f) Further Discussion

The present research incorporates Orbitrap high resolution mass spectrometry to allow for the identification of Hg-phytoplankton derived DOM complexes. Molecular composition of Hg-binding DOM can be confidently determined using Orbitrap HRMS. This study emphasizes the diversity in phytoplankton DOM composition between taxa at different photoperiods and how these DOM-Hg complexes can be detected and characterized using HRMS. It was showed that taxonomical differences in phytoplankton play a role in Hg binding and that greater similarities exist between Scenedesmus and Chlorella Hg-binding DOM than Chlamydomonas. The use of Orbitrap HRMS can be utilized for the putative identification of Hg binding DOM molecules.

Example 5: Effect of DOM Concentration on Bacterial Hg Bioavailability

I. Materials and Methods

Using bioreporter assays as described in Example 1, the impact of increasing concentrations of phytoplankton organic matter from Chlorella, Chlamydomonas, Scenedesmus and Euglena gracilis was evaluated. 5 nM of Hg in the absence of DOM was utilized as a calibration to observe a system lacking DOM in both oxic and anoxic conditions. Increasing concentrations of 0.1, 0.5 and 1 ppm DOM were allowed to bind to Hg for 1 hour prior to assays for Chlorella, Chlamydomonas, Scenedesmus. For Euglena, concentrations ranged from 1, 5, 10, 20 and 30 ppm DOM were used as concentrations >1 ppm did not significantly impact Hg mobility.

Orbitrap high resolution mass spectrometry was also conducted for Euglena gracilis at 1 and 30 ppm DOM to evaluate how DOM composition changes with concentration.

II. Results and Discussion

As DOM concentrations increase, there is a consistent and significant trend where Hg mobility decreases for all phytoplankton in both aerobic and anaerobic assays, except for Euglena gracilis in aerobic assays. Increasing concentrations >10 ppm DOM were shown to enhance Hg mobility into E. coli cells (FIG. 52). Orbitrap high resolution mass spectrometry spectra reveal that although some higher molecular weight DOM molecules are being produced by Euglena gracilis at 1 ppm DOM, these compounds are not preferentially released at higher DOM concentrations of 30 ppm DOM (FIG. 53). While not wishing to be limited by theory, these results show that the enhancement of low molecular weight molecules being selectively released by Euglena gracilis at higher DOM concentrations may shuttle Hg ions bound to these potential energy sources for smaller bacteria.

Example 6: Identification of Organic Ligands in Dissolved Organic Matter Produced by Scenedesmus obliquus Using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Laboratory grown cultures of Scenedesmus obliquus were obtained from the Canadian Phycological Culture Center (CPCC) in Waterloo, Ontario. The cells were grown using a bold basal media (BBM) at standard light regimes (16:8 h light to dark) fixed light intensity of 90-100 μmol photons m⁻¹s⁻¹ and fixed temperature of 21° C. constantly aerated in a growth chamber.

The toxicity of Cd (EC50=133 pbb or μL⁻¹ Cd) was determined using increasing concentration of Cd(NO₃)₂. Four algal cultures were grown in the presence of varying levels of Cd: control (0 μL⁻¹ Cd); EC20 (19.5 μL⁻¹ Cd); EC30 (46.4 μL⁻¹ Cd) and EC40 (78.8 μL⁻¹ Cd) starting at 1 million cells per mL for Replicate 1 and 2 million cells per mL for Replicate 2. The cells were harvested in early stationary phase for further analysis.

The supernatant (exudates) was separated from the cells by centrifugation. The exudates were filtered using a 0.45 μm Whatman filter. An aliquot that was made up of 50% methanol and 50% filtered exudates was adjusted to a pH of 6 before analysis using FT ICR-MS (FT-ICR ESI 7 Tesla, 16M; Range: m/z 200-2000; 200 scans in Negative Mode). Another set of exudates was spiked with 100 nM (Rep 1) and 300 nM (Rep 2) Cd (ICP-MS standard) at a pH of 6 and incubated overnight prior to analysis.

Data were exported and analyzed using Compass data analysis software (version 4.2, Bruker Daltonics). In order to detect Cd containing compounds the software Winnow⁴⁵ was used to detect 8 isotopologues of Cd (¹⁰⁶Cd, ¹⁰⁸Cd, ¹¹⁰Cd, ¹¹¹Cd, ¹¹²Cd, ¹¹³Cd, ¹¹⁴Cd and ¹¹⁶Cd). Only the peaks with a Winnow score of greater than 90% were further compared with respect to ratios of natural Cd abundances of at least ¹¹²Cd and ¹¹⁴Cd to confidently identify Cd molecular compositions using Compass data analysis Isotope simulation functions. In order to identify putative ligand complexes with Cd, the peaks with a Winnow score of greater than 90% were further compared to a modified database of known siderophores and their derivatives as well as different metabolomic online database such as Metlin, Chemspider, ChEBI, KEGG or Pubchem^(45,54-56) based on accurate m/z with an error ppm.

The number of complexes were quite similar between Rep 1 and Rep 2 of the exudates derived from EC30 treatment (Table 8). However, an increase of complexes was observed in Rep 2 in most of the treatments. The number of complexes found in Rep 2 was greater than in Rep 1, while not wishing to be limited by theory, because of the higher cell densities Cd concentration were used in Rep 2.

TABLE 8 Number of Cd Complexes Found by Winnow Software No. Complexes No. Complexes Sample Rep 1 Rep 2 EC20 57 167 EC30 63 62 EC40 41 99 Spiked Control* 63 104 Spiked EC40** 57 136 *Exudates produced by cells grown in the absence of Cd. **Cells grown with Cd (EC40 level) and exudates spiked and incubated with 100 or 300 nM Cd.

Five compounds were found in the exudates of two biological replicates of cells grown in the absence of Cd (“Control”) and at EC40 (Table 9). The proposed structures for the Cd-binding structures have been validated based on exact mass and natural Cd isotopic distribution. All proposed structures have been previously reported in microorganisms.

TABLE 9 Compound Details. Rep 1 Rep 2 Formula/Ligand Chemspider Ligand Sample complex m/z complex m/z Formula/Name ID Reference Spiked 956.3886 956.3891 C₃₇H₆₆CdN₁₀O₁₂ 8366570 Chemspider Control C₃₇H₆₆N₁₀O₁₂ 9345484 Chemspider Oligopeptides 9495360 Chemspider Spiked 878.4356 878.4351 C₄₃H₇₄CdNO₁₀ 58163504 Schmerk et EC40 C₄₃H₇₆NO₁₀ al., 2015¹⁰¹ Bacteriohopanetetrol cyclitol ether Spiked 940.37703 940.37839 C₄₆H₆₈CdNO₁₂ 28469198 Percopo et EC40 C₄₆H₇₀NO₁₂ al., 2013¹⁰² Azaspiracid-3 Spiked 958.3871 958.3879 C₄₅H₆₄CdN₈O₈ 10019079 Müller et al., EC40 C₄₅H₆₄N₈O₈ 2006¹⁰³ Brunsvicamide A EC40 958.3877 958.3878 C₄₅H₆₄CdN₈O₈ 10019079 Müller et al., C₄₅H₆₄N₈O₈ 2006¹⁰³ Brunsvicamide A

The molecular formula for oligopeptide complexes were identified (FIG. 54) by matching the top five Cd isotopes (¹⁰⁶Cd, ¹⁰⁸Cd, ¹¹⁴Cd) with their predicted intensities (bottom panel). Three potential candidates for the Cd-binding ligands found in exudates produced by Scenedesmus in the absence of Cd were found: L-Leucyl-L-asparaginylglycyl-L-lysyl-L-alanyl-L-leucyl-L-valyl-L-glutamic acid (ChemSpider ID8366570); L-Leucyl-L-asparaginylglycyl-L-lysyl-L-alanyl-L-leucyl-L-valyl-L-glutamic acid (ChemSpider ID8366570) and L-Valyl-L-asparaginyl-L-isoleucyl-L-glutam inyl-L-lysyl-L-α-glutamyl-L-isoleucine (ChemSpider 109495360), which have the following structures, respectively:

FIG. 55 shows an observed mass spectrum (top) compared to the corresponding predicted mass spectrum (bottom) for bacteriohopanetetrol cyclitol ether—Cd complex which ligand has the following structure:

FIG. 56 shows an observed mass spectrum (top) compared to the corresponding predicted mass spectrum (bottom) for Azaspiracid-3—Cd complex which ligand has the following structure:

FIG. 57 shows an observed mass spectrum (top) compared to the corresponding predicted mass spectrum (bottom) for Brunsvicamide A—Cd complex, which ligand has the following structure:

While the present application has been described with reference to examples, it is to be understood that the scope of the claims should not be limited by the embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety. Where a term in the present application is found to be defined differently in a document incorporated herein by reference, the definition provided herein is to serve as the definition for the term.

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The invention claimed is:
 1. A method of binding a metal ion in water, the method comprising: contacting the water with a fraction of dissolved organic material (DOM) to form a complex between the DOM fraction and the metal ion; and separating the complex from the water, wherein the fraction of DOM is a high molecular weight organic compound fraction of the DOM (HMW-DOM) having molecular weights ranging from 1800-3500 Da or a low molecular weight organic compound fraction of the DOM (LMW-DOM) having molecular weights ranging from 150-900 Da, and wherein the DOM is from phytoplankton.
 2. The method of claim 1, wherein the LMW-DOM comprises 3-methyldioxyindole, bellendine, linoleoyl, gluconapin, N-acetylleucyl-leucyl-methionianal, aminopentol, momordicilin, sulfanilamide, dihydroxypentatriaconta-2,4-dienoic acid, an oligo peptide (e.g. Ala-Thr-Leu-His; L-leucyl-L-asparaginylglycyl-L-lysyl-L-alanyl-L-leucyl-L-valyl-L-glutamic acid; L-leucyl-L-asparaginylglycyl-L-lysyl-L-alanyl-L-leucyl-L-valyl-L-glutamic acid; and/or L-valyl-L-asparaginyl-L-isoleucyl-L-glutaminyl-L-lysyl-L-α-glutamyl-L-isoleucine), 2-hydroxyheptanoic acid, (E)-penta-1,3-dien-2-ol, a diglyceride, glycerol triaprylate, 5,7,3′,4′-tetrahydroxy-3,6,5′-trimethoxyflavone, 9-octadecenoic acid, 1,2,3,4-tetrakis-o-(4-nitrobenzoyl)pentopyranose, ceramide, cefsulodin monobactam, 2,7,9-tricarboxypyrrolo(2,3-f)quinoline-4-ol-5-one, tetradecane-1, 1-(O-alpha-D-glucopyranosyl)-3-keto-(1,25R,27R)-octacosanetriol, 2,4-bis[4,5-bis(pentylamino)isoquinolin-1-yl]cyclobutane-1,3-dione, bacteriohopanetetrol cyclitol ether, azaspiracid-3, brunsvicamide A, siderochelin A, benarthin, chrysobactin, dihydroxybenzoic acid, rhizobactin, schizokinen, desferrioxamine, cyclic trichrisobactin, carboxymycobactin, exochelin, vibrioferrin, acinetoferrin, ferrioxamine or mixtures thereof.
 3. The method of claim 1, wherein the method is for remediation of wastewater having a metal ion to be removed and the water is wastewater.
 4. The method of claim 3, wherein the wastewater is domestic wastewater, urban wastewater, industrial wastewater or combinations thereof.
 5. The method of claim 4, wherein the industrial wastewater comprises effluent from a mining operation.
 6. The method of claim 1, wherein the separation comprises contacting the complex with a microorganism to sequester the complex.
 7. The method of claim 1, wherein the phytoplankton is a Chlorella sp., a Chlamydomonas sp., a Euglena sp., a diatom, a cyanobacteria, a protist or mixtures thereof, and/or the phytoplankton is Chlorella vulgaris, Chlamydomonas reinhardtii, Euglena gracilis, Euglena mutabilis, Scenedesmus obliquus, Thalassiosira weissflogii or combinations thereof.
 8. The method of claim 7, wherein the phytoplankton is Euglena gracilis.
 9. The method of claim 1, wherein the DOM fraction is isolated from DOM by field-flow filtration, ultrafiltration or ultracentrifugation.
 10. The method of claim 9, wherein the DOM fraction is isolated from DOM by a method comprising field-flow filtration.
 11. The method of claim 9, wherein the DOM is produced under conditions suitable to obtain an increased percentage of one or more desired metal ion-binding compounds in the DOM fraction.
 12. The method of claim 11, wherein the conditions comprise growing a culture of phytoplankton under conditions suitable to obtain the increased percentage of one or more desired metal ion-binding compounds in the DOM fraction.
 13. The method of claim 12, wherein the conditions comprise one or more of a desired medium, temperature, light, pH, ionic strength and metal concentration.
 14. The method of claim 13, wherein the conditions comprise varying the light regime.
 15. The method of claim 1, wherein the metal ion is a rare earth element, a divalent metal, a transition metal, or a divalent transition metal.
 16. The method of claim 1, wherein the metal ion is Hg²⁺ or Cd²⁺.
 17. The method of claim 1, wherein the LMW-DOM comprises molecular weights ranging from 300-900 Da. 